Why are signals reliable? Honesty depends on costs, sometimes

The role of signaling constraints in defining optimal marginal costs of reliable signals

The handicap principle was originally proposed to resolve the question of why, in their competition for mates, certain species invest in exaggerated ornaments that are often detrimental to their survival. Zahavi suggested that the traits that are most suitable to serve as signals are precisely those that require the burden of extra investment to increase in magnitude: that burden enables the signal to be correlated with the signaler’s quality. According to his model, the additional investment in signaling results in a functional advantage. It does so by providing more accurate information regarding the signaler as it increases the distinction between males of similar quality. There are a number of formalizations of this model, and experimental studies of the handicap principle have focused on testing them. Nonetheless, there is little consensus whether 1) ensuring reliability requires an additional investment or 2) traits that require a relatively higher investment to increase (have higher marginal costs) are selected as signals over those with lower marginal costs. Here, we present an agent-based mate choice model that quantifies the relative stability of signals with different marginal costs. Our model demonstrates how quality-independent constraints (in signal production and perception) affect the range of marginal costs for which a signal is informative. In turn, receiver preference for informative signals drives the selection of signals according to marginal cost. The presence or absence of signaling constraints can determine the outcome of costly signaling models and, thus, explain the different conclusions of Zahavi’s verbal model and its subsequent formalizations.

Content, cost, and context: A framework for understanding human signaling systems

Humans frequently perform extravagant and seemingly costly behaviors, such as widely sharing hunted resources, erecting conspicuous monumental structures, and performing dramatic acts of religious devotion. Evolutionary anthropologists and archeologists have used signaling theory to explain the function of such displays, drawing inspiration from behavioral ecology, economics, and the social sciences. While signaling theory is broadly aimed at explaining honest communication, it has come to be strongly associated with the handicap principle, which proposes that such costly extravagance is in fact an adaptation for signal reliability. Most empirical studies of signaling theory have focused on obviously costly acts, and consequently anthropologists have likely overlooked a wide range of signals that also promote reliable communication. Here, we build on recent developments in signaling theory and animal communication, developing an updated framework that highlights the diversity of signal contents, costs, contexts, and reliability mechanisms present within human signaling systems. By broadening the perspective of signaling theory in human systems, we strive to identify promising areas for further empirical and theoretical work.